Diacetals such as dibenzylidene sorbitols and nuclear-substituted derivatives thereof are useful compounds that are widely used as nucleating agents for polyolefin resins, gelling agents for various fluids, and so on. For taking full advantage of the characteristics of these compounds, the diacetal must first be dissolved or uniformly dispersed in a molten polyolefin resin or a fluid. However, these diacetals have strong self-agglomeration properties and also have a high melting point, so that uniformly dissolving or dispersing them is not easy in an industrial setting. Accordingly, the solubility and dispersibility of diacetals must be improved by one means or another.
There have been various proposals up to now aimed at ameliorating the above problems. Examples include a method in which a diacetal is treated at a temperature over its melting point or melting temperature, and a method in which a diacetal is reduced to an ultrafine powder in an effort to increase its dispersibility and make it more readily soluble (Japanese Unexamined Patent Publication No. H6-145431).
Nevertheless, (1) the first method, in which a diacetal is treated at a high temperature, causes the diacetal to undergo thermal decomposition, and therefore the nucleating agent does not reach its full performance potential, and there are also problems with coloration, odor, and so forth. (2) The second method (Japanese Unexamined Patent Publication No. H6-145431) involving reducing a diacetal to an ultrafine powder to improve its dispersibility and solubility leads to serious industrial problems such as dust explosion, an adverse effect on the workplace environment, re-agglomeration during storage, difficulty of transport (in particular, the difficulty of transport when discharged from a stock tank and difficulty of transport through pipes), decreased fluidity and other factors that make the material more difficult to work with. Also, this method requires expensive special pulverization equipment, and these and other problems have yet to be satisfactorily solved.
Another known method involves uniformly dispersing a substance for depressing the melting point in diacetal particles, thereby lowering the melting point of the diacetal (WO99/18108). This technique does not require that the diacetal be treated at high temperature or reduced to an ultrafine powder, and is an effective way to improve the solubility and dispersibility of a diacetal. However, there is still a need for (a) a further lowering of the diacetal melting point and (b) a lowering of the diacetal melting point to a practical level by using only a small amount of melting point depressant.
It is an object of the present invention to solve these problems by providing a diacetal composition with markedly improved solubility and dispersibility in various liquids and in various molten resins.
In particular, it is an object of the present invention to provide a diacetal composition which has improved solubility, dispersibility and storage stability of the diacetal, which can give a polyolefin resin molding with a less undispersed substance content and excellent transparency, and which contains a melting point depressing substance only in a small amount.